1. Field of the Invention
The invention relates to an organic metal complex, and more specifically to an organic metal complex applied in electroluminescent devices.
2. Description of the Related Art
Since 2000, development of organic light-emitting devices such as OLED has become popular. More than 160 enterprises are invested in OLED researches. The growth of shipping amount exceeds 175% per year. In 2004, the global sales achieved U.S. 4.46 hundred million, increasing 69.6% over the previous year. The OLED industry is continuously developing toward full-color and large-size panels. Display Search predicts, to 2008, the market scale will be increased to U.S. 50 hundred million.
OLED comprises multiple films, capable of luminescence. The C. W. Tang team of Eastman Kodak corporation utilizes Alq3 (tris-(8-hydroxy quinolinol) aluminum) and HTM-2 to prepare an OLED device, published in Appl. Phys. Lett. (p 913, 1987). Electrons and holes are confined in an organic layer to increase recombination thereof, achieving low driving voltage and high quantum efficiency. Thus, many corporations are invested in development of various luminescent materials. Additionally, OLED can also applied in, for example, cell phone panel, personal digital assistant (PDA) panel, car panel, computer screen, television screen, and illumination appliance applications due to self-luminescence (without backlight source), low cost, thin profile, high luminescence, no view angle limitation (>165°), high response speed, low driving voltage, and low power consumption.
In a conventional OLED structure, a transparent indium tin oxide (ITO) is formed on a glass substrate or plastic substrate, serving as an anode. A cathode is selected from a low work-function metal such as Mg/Ag or Al/Li. When a voltage is applied, electrons are injected into an emitting layer from the cathode and holes injected into the emitting layer from the anode. After recombination of electrons and holes, the device radiates. The luminescent color of the device is determined by the interior luminescent organic materials.
The luminescent materials are divided into fluorescent materials and phosphorescent materials. According to interrelated research, the complex formed by iridium, two cyclometalated ligands, and one negative-charge bidentate ancillary group possesses high luminescent efficiency. The luminescence of the complex can be varied from green to red by alternation of the cyclometalated ligand structures. The complex formed by iridium and three cyclometalated ligands also exhibits high green-light luminescent efficiency. Similarly, the scope of the luminescence can be extended from green to blue by alternation of the cyclometalated ligand structure and modification of number and location of electron-withdrawing groups and electron-donating groups.
In 1999, Forrest provides an organic phosphorescent material, “PtOEP”, doped in CBP by evaporation, published in Appl. Phys. Lett. 74, 442 (1999). Such devices provide a max external quantum efficiency of 5.6% and a CIE of (0.7, 0.3).
In 2001, Forrest further provides a red phosphorescent material containing iridium, “Btp2Ir(acac)”, doped in CBP, published in Appl. Phys. Lett. 78, 1622 (2001). Such devices provide a max external quantum efficiency of 7.0%, a max irradiation wavelength of 616 nm, and a CIE of (0.68, 0.32).
In 2003, Conon team provides a series of red phosphorescent materials, published in JACS 125, 12971 (2003). Among these, 1-(phenyl) isoquinoline(piq) is optimal, with a max external quantum efficiency of 10.3%, a max irradiation wavelength of 656 nm, and a CIE of (0.68, 0.32).
In 2003, Prof. Rai-Shung Liu provides a series of phosphorescent materials containing 1-(phenyl) isoquinoline(piq) host, having an irradiation wavelength within 595˜630 nm, published in Adv. Mater., 15, 884 (2003). The luminescent color is altered by addition of fluorine to 1-(phenyl) isoquinoline(piq), without deterioration of luminescent efficiency. Among these, Ir(piq)2(acac) and Ir(piq-F)2(acac) are optimal, with external quantum efficiency of 8.46% and 8.67% and CIE of (0.68, 0.32) and (0.61, 0.36) under 20 mA/cm2.
In 2003, Prof. Chien-Hong Cheng provides a reddish orange phosphorescent material containing dibenzo[f,h]quinoxaline serving as a ligand, “Ir(DBQ)2(acac)” and “Ir(MDQ)2(acac)”, published in Adv. Mater., 15, 224 (2003), with external quantum efficiency of 11.9% and 12.4% and CIE of (0.62, 0.38) and (0.60, 0.39), respectively.
In 2005, SANYO provides Q3Ir and (QR)2Ir(acac) containing diphenyl quinoxaline as a ligand, with an irradiation wavelength within 653˜675 nm. While 600 cd/m2, Q3Ir has a CIE of (0.70, 0.28) and the conventional high-purity red phosphorescent material, “Btp2Ir(acac)”, has a CIE of (0.68, 0.32). Such materials possess high luminescence, high efficiency, high CIE stability, and an absolute quantum efficiency of 50˜79%. Additionally, the luminescent time of Q3Ir is merely 1 μs at exciting state, ⅕ of Btp2Ir(acac).
Thompson provides a green phosphorescent material, “Ir(ppy)3”, doped in CBP, published in Appl. Phys. Lett. 75, 4 (1999), with a max external quantum efficiency of 8.0%, a max irradiation wavelength of 510 nm, and a CIE of (0.27, 0.63).
Improvement of OLED luminescent material performance is desirable, for example, material optics, electrochemistry, thermal stability, luminescent efficiency, and cost.